Radio Frequency Identification (RFID) systems typically include RFID tags and RFID readers. RFID tags are also known as RFID transponders. RFID readers are also known as RFID reader/writers or RFID interrogators. RFID systems can be used in many ways for locating and identifying objects to which the tags are attached. RFID systems are particularly useful in product-related and service-related industries for tracking objects being processed, inventoried, or handled. In such cases, an RFID tag is usually attached to an individual item, or to its label or package.
In principle, RFID techniques entail using an RFID reader to interrogate one or more RFID tags. The reader transmitting a Radio Frequency (RF) wave performs the interrogation. The RF wave is typically electromagnetic, at least in the far field. The RF wave can also be predominantly electric or magnetic in the near field.
A tag that senses the interrogating RF wave responds by transmitting back another RF wave. The tag generates the transmitted back RF wave either originally, or by reflecting back a portion of the interrogating RF wave in a process known as backscatter. Backscatter may take place in a number of ways.
The reflected-back RF wave may further encode data stored internally in the tag, such as a number. The response is demodulated and decoded by the reader, which thereby identifies, counts, or otherwise interacts with the associated item. The decoded data can denote a serial number, a price, a date, a destination, other attribute(s), any combination of attributes, and so on.
An RFID tag typically includes an antenna and tag electronics including a radio section, a power management section, and frequently a logical section and a memory. In some RFID tags the power management section includes a chemical energy storage device, such as a battery. RFID tags with a chemical energy storage device are known as active or battery-assisted tags. Advances in semiconductor technology have miniaturized the electronics so much that an RFID tag can be powered solely by the RF signal it receives. Such RFID tags do not include an energy storage device such as a battery, and are called passive tags. Passive tags often integrate the miniaturized electronics into an RFID Integrated Circuit (IC or RFID IC). Regardless of the type, all tags typically store or buffer some energy temporarily in passive storage devices such as capacitors.
Conventional RFID tag manufacturing processes include connecting the RFID IC to the antenna(s) using conductive epoxy. In general, attaching a bare RFID IC to an antenna leaves the chip exposed and vulnerable to mechanical damage. Using conductive epoxy leaves the inlay vulnerable to thermally induced failure.
The terminals of an RFID IC typically expose an input which is capacitive, and which must be compensated by an inductive tuning element at an operating frequency of the tag. Conventional matching circuits use a conductive loop, which is a part of the antenna. Unfortunately, in some types of tags, such as those that use slot antennas, it is difficult to build the loop into the antenna, resulting in compromised antenna designs or costly inductors that are attached to the antenna along with the RFID IC.